Enhancing Enzymatic Biodiesel Production Using Low-Cost CO2-Based Alkyl Carbamate Ionic Liquid and Ultrasound-Assisted Intensification

Enzymatic biodiesel production often faces challenges such as mass transfer limitations and enzyme sensitivity, resulting in low reaction efficiency. This study aimed to address these issues by integrating ultrasound technology with low-cost CO₂-based alkyl carbamate ionic liquids (ILs) as additives. Among the investigated carbamate ILs, N,N-diallylammonium N′,N′-diallylcarbamate (DACARB) demonstrated the highest fatty acid methyl ester (FAME) content in ultrasound-assisted biodiesel production catalyzed by Eversa Transform 2.0 at an optimal temperature of 50 °C. The addition of DACARB improved the solubility of immiscible reactants and enhanced lipase stability, maintaining high FAME yields even under ultrasound amplitudes of up to 100% and duty cycles of 20%. Enzyme hydrolytic activity assays revealed that DACARB activated the lipase, increasing enzyme activity by 33% through favorable alterations in the enzyme tertiary structure, as confirmed by fluorescence spectroscopy. Furthermore, employing a stepwise methanol dosing strategy with ultrasound at 40% amplitude and 5% duty cycle in the presence of 2 wt % DACARB achieved a FAME content of 91.3 wt % within 12 h, using only 0.2 wt % enzyme concentration. This study highlights the potential of DACARB as a promising additive to enhance the efficiency of ultrasound-assisted enzymatic biodiesel production, offering a promising solution to overcome current limitations in the process.